The Missouri Supreme Court on Tuesday upheld a 20-year-old state law requiring unaccredited school districts to pay for students to attend other nearby schools, a decision that could have implications for thousands of families.

The ruling focused on a case in which a parent wanted the then-unaccredited St. Louis Public School District to foot the bill for her two children to attend the neighboring Clayton schools. But the case has been closely watched by school-choice advocates and officials in other unaccredited districts, including the Kansas City school system, which have been hesitant to implement the law.

"This is big, potentially," said Brent Ghan, a spokesman for the Missouri School Boards' Association. He added: "It's going to be interesting to see how many students and families from unaccredited districts seek to transfer. It's certainly going to be challenging to the receiving districts who may not know how many kids to expect."

How quickly the ruling gets implemented remains to be seen. Because the decision came in June, some parents may try to transfer their children before the new school year begins in August. But it might be difficult for school districts to add staff - and classrooms - to accommodate an influx of students fleeing failing schools.

Some school districts had argued that the 1993 law violated the Missouri Constitution by imposing an unfunded state mandate. St. Louis County Circuit Judge David Lee Vincent III agreed in a May 2012 ruling in which he said the mandate was impossible for schools to comply with because of the budgetary consequences.

But the state Supreme Court overturned that decision in a unanimous ruling Tuesday. The high court said the 1993 law did not impose any new or increased educational requirement for schools. Rather, it said the law shifts the responsibility for educating particular students from one local district to another.

The Supreme Court also rejected the conclusion that the law was impossible to carry out - at least in this particular case brought by Gina Breitenfeld on behalf of her two children.

Attorneys for the St. Louis and Clayton schools had cited estimates during Supreme Court arguments in March that as many as 15,000 students - a little more than half the total enrollment - could have left the St. Louis school district under the transfer law after it lost its accreditation in 2007. But St. Louis regained provisional accreditation last year, making it no longer subject to the student transfer law. The court said the impossibility argument was thus speculative, and the schools clearly could accommodate Breitenfeld's two children.

The case has bounced around in court for years. Vincent first sided with the school districts in 2008, but the state Supreme Court overturned the decision two years later and ordered further proceedings, leading to Vincent's ruling for the schools last year and the latest appeal.

The high court on Tuesday sent the case back to the trial judge to reconsider his order that Breitenfeld pay $49,133 to Clayton schools to cover the cost of educating her children.

Attorneys for the Clayton and St. Louis school districts did not immediately return messages Tuesday.

Breitenfeld's attorney, Elkin Kistner, said Tuesday's ruling "vindicated our position all along" and could affect other school districts.

Education advocates also called the ruling significant.

"It's an obvious victory for children in failed districts," said Kate Casas, the state director for the Children's Education Council of Missouri, which advocates for school-choice measures. "They've been waiting on lists for seven years or five years or however long the school districts have been unaccredited."

She said Tuesday's ruling "is a clear signal to families in unaccredited districts that they should try again to get into a neighboring accredited district of their choosing."

Missouri currently has three unaccredited school districts - Kansas City and the smaller suburban St. Louis districts of Normandy and Riverview Gardens.

A spokesman for the Kansas City School District said officials there were reviewing the potential implications of the court ruling.

Ghan said the ruling could have an even greater effect when Missouri implements new accreditation standards in 2015 that could be more rigorous.

"It's possible we could see some other districts become unaccredited," Ghan said. "This ruling could come into play beyond just the urban areas of the state."